Cathode-ray tube coating apparatus



Dec. 1, 1953 J. H. DYNE ET AL CATHODE'RAY TUBE COATING APPARATUS Filed July 30, 1951 Fig.

4 Sheets-Sheet l i I b gm Q L M Q ImwAW-m INVENTORS JAMES H DYNE BY QORNELIUS M. BAKER ATTORNEYS Dec. 1, 1953 J. H. DYNE ETAL 2,660,978"

CATHODE-RAY TUBE COATING APPARATUS Filed July 30, 1951 4 Sheets-Sheet 2 IN V EN TORS JAMES H. DYNE CORNEL/US M. BAKER Dec. 1, 1953 J. H. DYNE ETAL CATHODE-RAY TUBE COATING APPARATUS 4 Sheets-Sheet 3 Filed July 50, 1951 INVENTORS JAMES H. DYNE CORNELIUS M. BAKER ATTORNEYS 1953 J. H. DYNE ET AL 2,660,978

CATHODE-RAY TUBE COATING APPARATUS Filed July so, 1951 1 4 Sheets-Sheet 4 INVENTORS JA MES H. DYNE CORNELIUS MBAKER FDWWW A T TORNE YS Patented Dec. 1, 1953 UNITED STATES ()FFICE 2,660,978 V cannons-RAY TUEE confine Arrliiui'iiiis James H; D'yne; Paclianack Lake; and Cornelius M. Baker, Clifton; N. J assignorls to Allen B; Du Mont Laboratories, Inc;, Clifton; N. 1.; a,

corporation of Delaware Application jun 36, 1951,'Scrial no; 239346 This invention relates to apparatus for make ing cathode ray tubes and more particularly to apparatus for applying fluorescent screens to such tubes.

When cathode ray tubes are inass produce on conveyors, sonic means must be provided to load the screen-forming solutions into the tube blanI-s; Some of these solutions may be pouredindiscriminately into the blanks but other solutions must be evenly dispersed within the blanks and; because of this, it has been found desirable to provide a rigid tubular member having a suitable dispersing nozzle that may be lowered into the tube blank. In order to do this, means must be provided to simultaneously move the tubular member with the tube blank as the blank is moved by the conveyor and great care must be taken not to introduce vibration into the conveyor which would result in forming imperfect fluorescent screens. Furthermore, the means for carrying the tubular member must return automatically to substantially the same starting location after the proper amount of liquid has been dispensed;

It is one object of the invention to provide proved apparatus for producing cathode ray tubes. I

Other objects are to; provide improved apparatus for applying the fluorescent screen to oath ode ray tubes and to provide apparatus which may be easily and accurately controlled with variations in the screen material, size) of the cathode ray tube blank or such other factors as are likely to be changed in the normal course of production within a short space of time. Other objects will be apparent after studying the fol= lowing specification and drawings in which? Figure 1 is a side-elevation view illustrating apparatus incorporating the present invention;

Figure 2 is a fragmentary perspective View of the apparatus illustrated in Figure 1; I 7

Figures 3 through 10 are fragmentary views of the apparatus illustrating the timing sequence of the operations involved in the normal use of the apparatus and Figure 11 is a diagrammatic illustration of the control system of the present invention.

This invention comprises dispensing apparatus operating simultaneously with a conveyor to form the fluorescent screens in cathode ray tubes in mass production. The dispensing apparatus, which is located adjacent one end of the con-' ve'yor and is preferably supported by aseparate framework to allow operators to reach the dispensing apparatus without introducing vibration into the conveyor itself, is adapted to introduce Glaims'a, (Cl. 118--2) predetermined amounts of a plurality of chemical solutions into each cathode ray tube blank on the conveyor to form a fluorescent screen therein; as described in United States patent application serial No. 100,543 to Albert Steadman, filed June 21, 1949, and assigned to the assignee of the present invention; In accordance with the disclosure of that application; a solution of barium acetate is first introduced into the tube blanks and there'- after a second solution comprising a inix'ture of potassium silicate and the fluorescent screen material is added.- In introducing these solutions into the cathode ray tube envelope in accordance with the present inv'ention a hose from a manifold in communication with a reservoir; conducts a metered amount of the barium acetate'solu tion into the continuously moving tube blanks and thereafter a predetermined amount of the second solution is evenly distributed into the first solution by" athistle tube which is in commune cation with a second reservoir containing the mixtureof potassium silicate and fluorescentniaterial. To accomplish an even distribution of the second solution; it is dispensed through a thistle tube which is lowered into the neck of the tube blank after the removal of the flexible hose. The thistle tube is supported by a carriage movable on rails which form part of a frameworkpref erabl'y structurally independent of the conveyor heretofore mentioned.- The power to more the carriage is" supplied by the conveyor through cogs attached to" the tube supports on the conveyor which intercept arms on the carriage. Automatic release of the carriage and return to the starting position following the introduction of the second solution into the tube blank is accomplished by inclining the carriage supporting rails so that the carriage is raised? simultaneously with its for: ward movement untilthe arms clear the dogs, thus allowing the carriage to coast to rest at the starting position. Raising and lowering of the flexible hose lines and thistle tubes out of and into the necks of the cathode ray tube blanks is accomplished by elevator mechanisms controlled by electrical switches which time the operations and which are interlocked to allow the solutions to new only it a catho'de ray tube is in position to receive theni.

Referring now' to the drawings and particu': larly to Figure i, there is illustrated a comma: ous conveyor ll having a plurality of spaced cathode ray tube holders [-2' preferably equally spaced along the longitudinal dimension of and attached to the endiess belt at. it is customary to mount theseholders three abreast at relatively closely-spaced positions along the longitudinal dimension of the conveyor belt, but more or less than that number may be used depending upon the desired production capacity. Thumb screws E4 or other suitable clamping devices securely clasp cathode ray tube blanks lfia, [6b and "3c in the holders which are attached to the belt IS. The thumb screws l4 are adjustable to the various sizes and types of cathode ray tube which are in current use. The belt 13 is driven by a motor ll connected to the input shaft of a speed reduction transmission I8, the output shaft of which in turn is connected to one of the beltdriving wheels [9 through suitable damping means, not shown. The belt I3 is supported for continuous movement on the wheels I9 which are rotatably mounted at opposite ends of the conveyor assembly.

The dispensing apparatus comprises a support structure 2! including a pair of rails 22 positioned on the support to be inclined upwardly relatively to the supporting surface of the conveyor belt, along the direction of its movement, as shown. While the support structure 2! is shown as being independent of the conveyor belt assembly to avoid transmission of vibration from the dispensing apparatus to the conveyor belt assembly, it will be obvious that it may form an integral part of the conveyor belt assembly. A carriage 23 provided with rollers 26 engaging the rails 22 reciprocates on the rails in substantially the direction of movement of the conveyor belt. A pair of generally V-shaped arms 2d are disposed on opposite sides of the carriage 23 and engage the inner sides of the rails 22 to prevent the carriage from slipping from the rails. The arms are provided at their lower ends with hardened catches 26 which engage with similarly hardened cogs 27 secured on the holders 12 when the carriage is at its initial or normal position of movement on the rails.

Referring now to Figures 1 and 2, there is secured at the top of the structure 2|, a manifold 28 and three spaced hose lines 29a, 29b and 290 for dispensing a barium acetate solution. The hose lines are supported by and raised and lowered into and out of the necks of the tubes it by a frame 3!, see particularly Figure 2. The second solution comprising a mixture of potassium silicate and fluorescent material is stored in three vessels 32a, 32b and 320 mounted at the top of the structure 2! and is dispensed through the thistle tubes 33a, 33b and 330 which are secured in spaced relation on the carriage 23. The thistle tubes 33 are raised and lowered by a frame 34.

Referring now more particularly to Figure 2, there is illustrated in detail the dispensing apparatus including the elevator mechanisms for raising and lowering the frames 3i and 34. In the present embodiment, air cylinders 36 and 3'! slideably supporting pistons connected respectively to the frames 3| and 3d raise and lower the frames. Movement of the frame 34 is guided in the carriage 2% by a pair of bearing rods 33 vertically supported at opposite sides of the carriage. The base of the carriage 23 is maintained substantially level and in parallel relation with the conveyor belt by supporting legs 39 and H of unequal length in order that the thistle tubes may drop perpendicularly into the necks of the tubes Hi.

In Figure 2, the tube I6 is shown receiving a charge of barium acetate solution by means of the hose line 290 inserted in the neck which is located on the holder 12 by the clamp 42 secured thereto so that the line 29 will drop into the neck without striking the rim. As the conveyor moves the tube holder l2 in the direction shown by the arrow, the neck of the cathode ray tube blanks enters an inverted trough 53 comprising a pair of perpendicularly disposed adjacent flaps as which prevent excess liquid from running down the outside of the trough and into the conveyor mechanism.

Attached to the support 2| is a metering apparatus for dispensing the barium acetate through the hose lines 29a, 29b and Ella. The metering apparatus comprises the manifold 2s and a plurality of solenoid operated valves 280., 461) and We of which only one 480. is shown in the drawing. A solenoid Ma for operating the valve 46a is located directly above the valve itself and is controlled by an electric current from a timer 4% in response to signals from microswitches which are not shown in this figure. In this connection, it will be understood that each of the valves 46b and 460 is controlled by a solenoid and timer similar to the solenoid and timer ll'a and 48a respectively. A continuous and even pressure is maintained in the manifold 28 and the metering of the proper amount of barium acetate solution therethrough is accomplished by timing the open period of the valves 35s, 3% and 460 rather than by allowing the fixed amount of solution to accumulate in a separate reservoir. This results in easier changeover from one size of cathode ray tube blank requiring a certain amount of barium acetate to another size tube blank requiring a different amount since the amount can then be determined by the setting of the timers ita, 48b and tile rather than by changing to a reservoir of a different size which would entail disconnecting a number of hose lines. However, using a separate reservoir to meter the barium acetate results in a somewhat more accurate control of the volume thereof supplied to each tube blank and the separate reservoir may thereby be used as an alternative to the timer controlled process, particularly where precise measurement of the volume of liquid is required.

Supported on the carriage 23 beneath the thistle tubes is a drip trough 5i comprising a bottom member 52 having holes, not shown, aligned with the necks of the tube blanks and a top piece 53 having similar holes. Upon closure of a limiting switch, not shown, air actuated device 55 pushes the top piece 53 to the right so that the holes therein are aligned with the holes on the bottom piece and the necks of the tube blanks. When the two pieces are so aligned, a switch 56 is closed which allows the air cylinder 31 to lower the frame 34 so that the ends of the thistle tubes 33 pass through the aligned holes and into the necks of the tube blanks. The purpose of providing two relatively slideable members 52 and 53 is to cut off the drippage from the thistle tubes 33 as shown.

Referring now to Figures 3 through 10, there is illustrated the sequence of operation of the air actuated devices 35 and 31. As one of the tube blanks comes into position under the bar-i lll'll acetate dispensing member Ziic in Figure 3, a microswitch 5! shown in Figures 1 and e as being supported on the conveyor belt assembly above the returning belt, is closed by movement of a bar 58 secured on the underside of the holders l2. It is possible to use any part of the conveyor as a timer because the entire mechanism operates as a unit and each of the longitudinally spaced holders i2 is equally spaced from ad-jae cent holders; equally spaced, it would be obvious that it will be necessary to support the microswitch 5'! on the conveyor assembly so that it will be actuated as the row of tube blanks moves into position under the dispensing members 29a, 29b and 290. A plurality of microswitches 59 are attached at laterally spaced points on support 2i, each mi croswitch being positioned so that the arm 60 thereof is actuated by contact with the necks of each of the laterally spaced tube blanks I6.

In Figure 5, the tube 16 has moved to the right and has received its full charge of barium acetate solution through the hose 2% which has moved upwardly as indicated by the arrow in response to a signal from the microswitch 6! shown in Figure 6. It will also be noted that the catch 28. has made contact with the cog 21 initiating the above-mentioned movement of the carriage .23;

In Figure 7, the frame 34 has lowered in ree sponse to a signal from microswitch $2, in Figure 8., and the second solution of potassium silicate and fluorescent material is being disseminated through the dispersing nozzle on the end of the thistle tube 330. Another group of laterally spaced microswitches 63 supported by the frame 2| is operated by the necks of tube blanks in a manner similar to that described in connection with microswitches 59. While the microswitches 59 and 63 act on the timers to start the flow of the solutions through the hose lines 29a, 2th

and 29c and thistle tubes 33a, 33b and 330 respectively, they also act as interlocking switches to prevent the flow of these solutions in the event that the operator has failed to place a tube blank in any particular holder.

In Figure 9, the frame 34 has moved up again as indicated by the directional arrow and the carriage 23 has risen almost enough to allow the catch 26 to clear the cog 21. Raising of the frame 34 is accomplished by the air cylinder 3?, shown in Figure 2, in response to a. signal from the microswitch 65, shown in Figure 10. A shock absorber 66 is attached to the frame 2.! to index the initial or starting position of the carriage :23 and to dissipate the momentum or shock of impact of the carriage 23 when it returns to its initial position.

After the thistle tubes have been raised as shown in Figure 9, the cathode ray tube blanks as travel up to the far end of the conveyor H, are tilted to decant the excess liquid as shown in Figure 1, and return on the underside of the conveyor to the starting position at the left hand end thereof where they are removed by the operator and fresh-blanks are put in place. The entire operation can be accomplished by a sin-.- gle operator in place of the three or four who would normally be necessary if the screen-forming materials were hand loaded into the tube blanks as has been the custom heretofore.

In the diagrammatic representation in Figure 11, the interconnections between parts of the dispensing apparatus which are operated electrically and those which are operated by air pressure are diagrammatically shown to the exclusion of the conveyor II and the carriage 23 of Figures 1 and '2. Figure 11 may be considered as supplementary to Figures 3 through in illustrating the operation of the dispensing apparatus.

The operation of the circuit in Figure 11 starts withthe actuation of microswitch 51 by the bar 58. Microswitch 51' connects electrical Where the tube holders are not power from the source 65 to. a solenoid 61 con trolling thev operation or the four-way air valve 68' which connects a. source 59 of compressed air selectively to. either side of the piston, now shown, in the air cylinder 35. Energizing the solenoid Bl; operates the valve 6.8 to apply compressed air to the side of the piston which causes lowering of the. frame 3i thereby dropping the hose lines 29a, 2%. and 290 into the necks of the tube blanks. Since the operation is the same for each of the three laterally spaced columns of tube blanks, reference will be limited to the apparatus associated with the column of tube blanks identified by the subscript a through out the description of Figure 11 in order to simpliiy the description. After the hose line 25a descends into the neck of the tube Iiia, movement of the. conveyor l l, which is not shown in this figure, causes the neck of the tube Eta to press on the arm Sta thereby actuating the microswitch 59a which connects electrical power from the source H to the timer its and from there to the solenoid 41a which opens the valve eta. As has been heretofore mentioned, it will be understood that similar timers and solenoids will be associated repectively with dispensing members 2922 and 290 as described in connection with dispensing member 29a. While the power source H is illustrated as being independent of the power source 65, it will be understood that electrical power for the system may be supplied from a common source. Opening valve 653a allows barium acetate solution to flow from the manifold 28 to the tube Ida through the hose line 2961.. At the end of a predetermined length of time when the required amount of barium acetate has passed into the tube lea, the timer 48a shuts off the electrical power to the solenoid lla which, in turn, closes the valve i-iia.

Shortly thereafter, the bar 58 actuates the microswitch ti which connects the source of power 65 to energize the solenoid l2. Solenoid 12 operates the valve 53 in such a manner as to apply compressed air from the source 59 to the lower side of the piston in the air cylinder 35 and, at the same time, to connect the upper side of the piston, i. e. the side to which compressed air was applied by operation of the solenoid hi, to the atmosphere by means of the exhaust it. This operation raises the piston in the cylinder 36 thereby raising the frame 3! and lifting the hose line 29a clear of the tube i605.

Continued movement of the conveyor l l causes the bar 58 to actuate the microswitch 62 which connects electrical power from the source is to energize the solenoid 16 which controls the operation of another four-way valve ll similar to valve 68. Operation of the valve ii by the solenoid it supplies compressed air from the source 6% to the cylinder 54 in such a way as to push the plate 53 against the microswitch "it as was described in connection with Figure 2. When the microswitch 55 is operated by the plate 53, electrical power is connected from the source it to a solenoid '59 which is one of two solenoids operating a third four-way valve M. This valve is similar in operation to the four-way valve 63, and the solenoid '19 operates it in such a way as to supply compressed air from the source 5% to the cylinder 3'? to force the frame 3 1 down, thereby carrying the thistle tube 33a into the neck of the tube [6a.

Very shortly after the thistle tube 33a descends into the neck of the tube Eta, the continued motion of-theconveyor H shown in Figure 1 causes the tube its to actuate the microswitch 63a by means of the lever 82a. Actuation of this microswitch connects a source of power 83 to a timer Sta which controls the power applied to a solenoid lite. In this connection, it will be undei stood that similar timers and solenoids are associated with thistle tubes 33b and 330 for the control of the dispensing of solutions therethrough. The solenoid 86a controls a three-way valve S'la which may be opened to admit passage of the solution containing the fluorescent screen material and the potassium silicate mixture from the reservoir 32a to the thistle tube 33a or distilled flushing water from a manifold 8 to the thistle tube 33a or it may be closed entirely. The operation of the timer 86a is therefore somewhat more complex than the operation of the timer 48a in that it is necessary to control the operation of the solenoid 85a to three positions. The sequence of operation starts with the opening of the valve filo to admit the above-mentioned second solution from the reservoir 32a to the thistle tube thence to the cathode ray tube blank its. At the end of a predetermined length of time, the solenoid 36a switches the valve 8%. from the reservoir 32a to the distilled water manifold 88 to flush out the last few drops of the fluorescent material mixture in the thistle tube After sufficient flushing water has been admitted, the solenoid Eta switches the valve 87a to the cutoff position.

During the flushing operation, the bar 58 moves into position to actuate the microswitch which connects electrical power from the source it to the solenoid 89. This solenoid operates the four-way valve 8| to raise the piston in the air cylinder ill in the same manner as the valve til operates on the air cylinder to herein above described. As the frame 3 3 moves upwardly, it actuates the microswitch at which applies power from the source it to the solenoid 92. lhis solenoid acts on the four-way valve ll which controls the return of the tray 53 by means of the air cylinder s4. Since this tray cannot be returned until the thistle tubes 33a have been lifted clear of it, there is no danger of the trays clipping on the end of the thistle tubes.

One complete cycle of operation of the dispensing apparatus has been described. It will, of course, be obvious to those skilled in the art that modifications may be made in the operation. For instance, the hose lines 2% may be placed on ie carriage 23 in Figure l and raised and lowered simultan ously with the thistle tubes $3 by a single cylinder 3i, thus eliminating the need for air cylinder 3% and also eliminating the need for the flexible lines 29 which may be replaced by tubes similar to the thistle tubes 33 except that they need not have dispersing nozzles on the ends thereof.

The operation of the machine as a unit is initiated by applying ower to the motor it which in turn drives the conveyor belt i3. As the conveyor belt with its holders l2 carrying the processed tube blanks it move along their return path to the left-hand end of the machine as viewed in Figure i, an operator stationed at that end releases the processed tube blanks and substitutes unprocessed blanks for processing. As the blanks on the holders move with the belt toward the right-hand end of the machine, barium acetate is introduced into the blanks through the hose lines in the manner hereinbefore described. Thereafter, as the blanks on the holders continue to move toward the right-hand end of the machine the catches 26 supported on arms 24 g, engage the cogs 21 secured on the holders it. With continued movement of the belt thereafter, the carriage 23 moves with the belt, holders, and tubes along the inclined rails 22. During this simultaneous movement of the tubes and carriage, the potassium silicate solution with iiuorescent material dispersed therethrough is introduced into the tubes through the thistle tubes 33 in the manner hereinbefore described. [is the carriage Z3 approaches the right-hand end of the inclined rails 22, the catches become disengaged from the cogs 27 permitting the carriage 23 to move by the force of gravity back along the i clined rails to its starting position where the sequence of operations is repeated for the next following row of tubes. After the tubes have received the different solutions, they continue to move with the conveyor toward the right-hand end of the machine Where they are tilted as the belt follows the contour of the supporting wheel it. As the tilting of the tubes is increased by continued movement of the belt, the liquid slowly decanted from the tubes without (iiuf oing the settled film of fluorescent mat .l. Thereafter the tubes return toward the le thand end of the machine where they ar moved by the operator.

What we claim as novel and desire to by Letters Patent of the United States is:

i. In combination, a conveyor for so orting and moving a plurality of spaced receptacles thereon, a support for said conveyor, a

rails inclined to the horizontal plane of said support to permit the weight of said ce to return it the lower position of for interconnecting said carriage eyor to move said carriage through a mined with said conveyor and release said carriage, and dispensing mounted on said carriage movable with ea ceptacles for introducing fluorescent forr ing materials into said receptacles.

2. in combination, a conveyor, a plurality of spaced supports mounted on said convey 1', said supports being adapted to receive cathode ray tube blanks, a carriage positioned adjacent conveyor and movable in directions parallel with the direction of movement of said conveyor, cogs secured to said supports, a catch secured to said carriage, said cogs and catch being interconnectable to provide simultaneous movement of said conveyor and carriage, supporting means for said carriage, said supporting means being inclined to the surface of said conve or to provide a predetermined amount of s ultoeous movement of said carriage and said conveyor and thereafter disengage said cogs and catch return said carriage to its initial position, indexing means for determining the starting position of said carriage, and dispensing means mounted on said supporting means for said carriage and having liquid conducting means movable with said carriage for introducing predet mined amounts of fluorescent screen-forming solutions into said blanks.

3. In apparatus for forming fluorescent on cathode ray tubes, a continuous conveyor, a support for said conveyor, a plurality of spaced cathode ray tube blank holders mounted on conveyor, cogs attached to said holders, 2.- carriage, a support for said carriage, said support including a pair of rails inclined to said conveyor and on W. ich said carriage moves. arms ar uv.

and said carriage returns by force of gravity to its initial position, shock absorbing means attached to the carriage support for determining said initial position of said carriage and absorbing the momentum of said carriage as it returns to said position, and dispensing means secured to said support for said carriage and having means movable with said conveyor and including separately controlled dispensing members for adding a plurality of fluorescent screen-forming solutions to said tubes at predetermined intervals during'the simultaneous movement of said conveyor and carriage.

4. In combination, a continuously moving conveyor, a support therefor, cathode ray tube blanks mounted in holders attached to said conveyor and moving therewith, and dispensing apparatus for supplying fluorescent screen-forming solutions to said blanks, said dispensing apparatus comprising a first source of a first solution and a flexible hose connected to said first source to convey a predetermined amount of said first solution to each of said tube blanks in succession, said first source being mounted on said support, a first elevator attached to said support and to said hose to lower said hose into said tube blanks in succession and subsequently raise said hose again, a second source of a second solution, rigid tubing connected to said second source, a carriage to transport said tubing over said conveyor and parallel to the motion thereof, cogs attached to said conveyor and catches attached to said carriage to transmit motive power from said conveyor to said carriage, a second elevator mechanism to lower said tubing into said blanks in succession following the removal of said hose therefrom in order to bring the end ofsaid tubing into proper spaced relation to disperse a predetermined amount of said second solution over the surface of said first solution, inclined rails forming part of said dispensing apparatus and supporting said carriage, said rails being inclined upward in the direction 10 of motion of said conveyor and the slope of the inclination being sufiicient to raise said arms above said cogs to free said carriage to coast back to the starting point.

5. In apparatus for forming fluorescent screens on cathode ray tubes, a continuous conveyor, a plurality of spaced cathode ray tube blank holders mounted on said conveyor, means for driving said conveyor, cogs secured to said holders, a carriage, a support for said carriage, said support including a pair of rails inclined to the surface of said conveyor and on which said carriage moves, a pair of spaced arms extending downwardly from said carriage and between said rails for guiding the movement of said carriage on said rails, catches attached to said arms and inter-engageable with said cogs in one position of said carriage on said rails to transmit motion from said conveyor to said carriage and move said carriage through a predetermined distance on said rails where the upward inclined movement of said carriage with respect to said conveyor disengages said catches and cogs and said carriage returns by force of gravity to its starting position, shock absorbing means attached to the carriage support for indexing the initial position of said carriage on said rails and absorbing the momentum of said carriage as it returns to said position, first dispensing means mounted adjacent said conveyor and automatically movable into and out of said tubes at predetermined time intervals for dispensing a predetermined amount of one fluorescent screen-forming solution therein, and second dispensing means mounted on said carriage and subsequently automatically movable into and out of said tubes to disperse in said first-mentioned solution a predetermined amount of a second fluorescent screen-forming solution.

JAMES H. DYNE. CORNELIUS M. BAKER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,333,023 Sykes et al. Aug. 21, 1945 FOREIGN PATENTS Number Country Date 155,395 Great Britain Dec. 23, 1920 

